Gd ₂O ₂S:Dy ³⁺  phosphors were synthesized by a homogeneous precipitation method from Gd ₂O ₃, Dy ₂O ₃, H ₂SO ₄ and Urea starting materials. The characterizations of Gd ₂O ₂S:Dy ³⁺  phosphors were investigated by means of XRD, FE-SEM and PL spectra. XRD analysis shows that the precursor can be transformed into pure Gd ₂O ₂S powder by calcining at 900 ℃ for 1 h in hydrogen. FE-SEM observation shows that the Gd ₂O ₂S powder particles are quasi-spherical in shape, with a mean particle size of about 300~500 nm. Photoluminescence (PL) spectroscopy reveals that the main and second emission peaks are located at 579 nm and 488 nm under 270 nm UV light excitation, which corresponds to the  ⁴ F _9/2→ ⁶H _13/2 and the ⁴F _9/2→ ⁶H _15/2 transitions of Dy ³⁺ ions, and both transitions of Dy ³⁺ ions have a single exponential decay behavior. The quenching concentration of Dy ³⁺ ions is 1 %. The CIE coordinate and the color temperature of (Gd _0.99,Dy _0.01) ₂ O ₂S phosphor are (0.308, 0.379, 0.313）and 6 464 K respectively.

The microstructure of pearlite spheroidized 20g steel during tensile deformation was investigated with field metalloscope. SEM images of the specimen were taken after deformation. The results show that during tensile deformation, pearlite spheroidized 20g steel got deformed in some of its grains. It causes a large amount of glide bands, and piles-up at the grain boundary. Some of other grains start to deform, which form favorable orientation in order to complete further deformation. During tensile deformation, microcracks generate at the pearlite on the edge of the specimen. Microscopic voids generated at the ferrite and pearlite grain boundary inside the specimen, then extend and connect to microcracks, it shows as transcrystalline and intercrystalline fracture.

 

The 400 MPa ultrafine grained steel strip with thickness of 8 mm was connected by CO2+Ar arc welding under single-pass welding and double-pass welding, and the low-temperature toughness for weld joints was investigated by series impact test. The experimental results show that the low-temperature toughness for weld is worse among the weld joint. The low-temperature toughness for weld joint by double-pass welding is better than that of single-pass welding, and its heat affected zone(HAZ) is decreased because smaller heat input reduces grain growth coarsening.